Okay so, Sephiroth appears to have the white materia and the static effect here means this is from Cloud's pov. I believe this is Sephiroth taunting Cloud over Aerith's "death". With Rebirth having Cloud remember Zack by himself, along with SE releasing CCR after Remake, I think the story is shifting from the mystery of "Was Cloud really in Nibelheim?" to "Did Cloud really save Aerith?" I still think Nibelheim will play into Cloud's mental collapse but it won't be as damaging as the reveal of Aerith's "death" - perhaps Sephiroth will even convince Cloud that he himself killed her. I mean, Cloud is literally starting the game believing Aerith is heading back to the Forgotten City to stop the meteor, this alone is a massive deviation from OG (as much as people love to pretend this is the same story) so the Northern Crater has to adjust to this change.
I've seen people say this scene is where Cloud breaks down but judging by the fact that Barret is visible in the background, I think this is after a boss fight against Jenova, based off that purple goo on the floor anyway. I'm still not 100% sure whether the scene of Barret and the party in the third photo comes before or after this scene of Cloud. With how short it is, it looks like Barret is calling the others over. My guess is after this fight, Cloud gets visions of that scene of Sephiroth and perhaps even goes into "puppet mode", leading into a boss fight against Cloud (this is wishful thinking my half, i really want a fight against a unhinged Cloud).
Now this scene is really interesting, I've read people theorising Sephiroth is impersonating Aerith here and I can definitely see where they're coming from. My only real argument against it is that Rebirth shows Sephiroth is able to get Cloud to bend to his will by his own presence without putting on a disguise so I don't really see what motive he might have to do it here. My guess would be he impersonates Aerith to trick Cloud into handing over the black materia which in Cloud's pov is him handing over his hollow materia to Aerith. But again, in Rebirth, Sephiroth was able to make Cloud hand over the black materia without a disguise.
That being said, since Cloud has the black materia fused into his sword, he won't be leaving it behind to a party member like he did in OG so maybe this scene is him striking some sort of deal with Sephiroth/ Sephiroth manipulating Cloud to summon the meteor himself.
